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The Fourneyron Ttirbine.

723

Turbines, formerly including only horizontal types, is the
term now applied to all water wheels in which a relative move-
ment of the water to the wheel causes reaction. The Reaction
wheel, Fig. 709, is the earliest form, being a turbine without
guide blades. The casing A, or wheel proper, has tangential
nozzles BBB, through which the water leaves, entering at c; its
reaction on A thereby producing motion. If the best velocity,
that due to head, be employed, an efficiency of '6 is attainable;
but otherwise there is considerable waste of energy. This fact
led to the introduction of guide blades and curved vanes, and the
invention of the true turbine.

Fig. 709.

The Pourneyron Turbine, Fig. 710, is an outward-flow and
also a pressure turbine, the wheel passages being kept full. A, the
wheel, is keyed to shaft B to transmit the power, and the water
flowing downward from c is so deviated by fixed guide blades DD,
that it enters the wheel nearly at a tangent. The wheel vanes are
so curved that the flow is then changed to a radial direction, the